Muscle spindles form in paralyzed but not in aneural hindlimbs of fetal rats.
The necessity of innervation and/or neural activity for the formation of muscle spindles was investigated by treating fetal rats with neurotoxins on embryonic day 16 or 17 (E16-17), one or two days prior to the onset of spindle assembly. The neurotoxin-treated soleus muscles were examined on E21 for the presence of spindles and immunocytochemical expression of the slow-tonic myosin heavy-chain (MHC) isoform, which is characteristic of intrafusal fibers. Irreversible destruction of sensory and motor nerves by beta-bungarotoxin prevented the formation of spindles and expression of the slow-tonic MHC. Abolishment of nerve and muscle activity by tetrodotoxin did not block the spindle assembly or expression of the slow-tonic MHC. Thus, the formation and differentiation of spindles is dependent on innervation, but is independent of activity in nerve fibers or muscle cells.
Kucera
J
J
Department of Neurology, School of Medicine, Boston University, MA 02118.
Walro
J
J
D000818:Animals; D002038:Bungarotoxins / Q000633:toxicity; D005260:Female; D005333:Fetus; D006614:Hindlimb; D009132:Muscles / Q000187:drug effects / Q000196:embryology / Q000473:pathology* / Q000503:physiopathology; D009498:Neurotoxins; D010243:Paralysis / Q000139:chemically induced / Q000473:pathology*; D011247:Pregnancy; D051381:Rats; D011919:Rats, Inbred Strains; D013779:Tetrodotoxin / Q000494:pharmacology
D002038:Bungarotoxins; D009498:Neurotoxins; D013779:Tetrodotoxin